In an apparatus for detecting feature point in the related art, there is a method of detecting a small number of feature points such as a nose and eyes on a face image and then setting a new different feature point using the positions of the detected feature points as disclosed in Japanese Application Kokai 2004-265267.
There is also a method of limiting the range of searching the different feature point using the positions of the facial feature points detected on the image as disclosed in Japanese Application Kokai 10-86696.
In these methods, the detection of the second feature point is achieved by using a relative positional relationship with the detected first feature points on a stored two-dimensional image. However, there is a problem such that the second feature points cannot be detected correctly because the relative positional relationship of the feature points calculated when the face is oriented to the front does not indicate correct positions when the orientation of the face has changed.
As an example of the problem shown above, a method of detecting a point corresponding to a mouth center, which is a midpoint between the left end and the right end of the mouth, will be considered. As disclosed in Japanese Application Kokai 2003-187247, there is a method of detecting the lip area by sorting color components and defining the both ends of the lip area as lip ends, and the midpoint of the lip ends as the mouth center. When the face is oriented to the front, the mouth center is likely to be almost the same as a midpoint between the mouth ends. However, when the orientation of the face has changed, or when the shape of the portion around the mouth has changed because the facial expression has changed, the position of the mouth center dose not match the midpoint, and hence the position of the mouth center cannot be obtained correctly.
As described above, there is the method of detecting the first feature point and detecting the second feature point using the result of the first detection in the background of the detection of a feature point. However, since the relative positional relationship between the feature point obtained in the detection of the first feature point and the feature point obtained in the detection of the second feature point is defined on a two-dimensional image, when the orientation of the target object at the moment when the relative positional relationship is defined is different from the actual orientation of the target object, correct detection of the feature point cannot be achieved.